1. Field of the Invention
The present invention concerns the field of material exchange or molecular or particle separation. In the above preferred field, the subject matter of the invention has a particularly advantageous application in the field of nanofiltration, ultrafiltration, microfiltration, filtration or reverse osmosis.
2. Description of the Related Art
In the material exchange field, an appliance generally comprises a filter module with an inlet connected to a supply line for a fluid medium and an outlet connected to a fluid medium outlet line. The filter module generally comprises a series of channels arranged in a rigid support inside which the fluid medium circulates.
In general, one or more channels are arranged inside tubular filter elements. Each filter element is constituted by a porous support inside which one or more channels are arranged, the internal surface of which is provided with at least one separating layer, the nature and morphology of which are adapted to separate molecules or particles contained in the liquid medium circulating in the channels. Such a filter element separates molecular species or particles from the substances to be treated by a sieving effect, where all the molecules or particles with a diameter greater than the pore diameter of the separating layer are stopped. The filter element thus divides the incoming volume into a first volume termed the "filtrate" or "permeate" containing molecules or particles which have passed through the filter element and into a second volume containing molecules or particles which have been held back by the filter element. It is thus known for an exchange apparatus forming a filter module to be constituted by a series of tubular filter elements placed side by side inside a housing. It can thus be constituted by a module containing 252 tubular filter elements with an external diameter of 10 millimeters (mm) or by 37 tubular elements with an external diameter of 25 mm.
However, the fluid to be treated includes heterogeneous elements such as bubbles or clumps of matter. Such heterogeneous elements, in a variety of sizes, can plug the circulation channels and the channel is then no longer accessible to fluid. This results in a reduction in the exchange or filter surface. Further, it has been found that such heterogeneous elements can cause the destruction of the support in which the fluid circulation channels are arranged. Such modules must be cleaned using chemical reactants which attack the matter deposited inside the channels to detach them from the porous support. However, a relatively large heterogeneous element cannot be destroyed by chemical reactants. Rather, the heterogeneous elements degrade causing a change in the volume of the heterogeneous elements which can then press on the channel walls to such an extent that the support breaks.
It has also been noticed that heterogeneous elements such as bubbles can cause destruction of the supports. Air bubbles appear in the medium to be treated due to poor filling of the appliance or to cavitation in the circulation pumps or to degassing of the fluid. If the bubbles remain in the appliance, their internal pressure can increase as they pass through the inside of the exchange module. Such an accumulation of energy inside the bubbles can cause them to depressurize all at once as a water hammer. The wave developed by the water hammer can cause the destruction of the exchange supports.
In the heat exchanger field, it is known to install an apparatus formed from a plate pierced with holes upstream of the exchanger tube inlet, the diameter of the holes being less than the cross section of flow of the exchanger tubes.
However, using such a plate in a filter module would not be entirely satisfactory. The interposition of such a plate in the fluid circulation path would cause a reduction in the performance of the module due to the pressure drop created. Further, it must be considered that the holes in that plate tend to be plugged relatively frequently by heterogeneous elements which can be deposited on the plate. This results in a drop in performance and maintenance operations must be carried out relatively frequently.